Baculoviruses are a group of rod-shaped, enveloped, double-stranded DNA viruses having a circular, supercoiled genome varying from 90 to 160 kb in size. They have been successfully used for efficient expression of engineered proteins. A baculovirus system is more attractive than other protein expression systems because of its high level expression, posttranslational modification ability, and safety for use in humans (Smith et al., 1983, Mol. Cell Biol. 3, 2156-2165).
However, the yield of engineered protein prepared from a baculovirus system is not satisfactory. First, the peak time for engineered protein production varies from 2 to 6 days post infection (dpi) (Chatterji et al., 1996, Gene 171, 209-213; Liebman et al., 1999, Biotechniques 26, 36-42; and Pennock et al., 1984, Mol. Cell Biol. 4, 399-406). These variations may result from the concentrations of viruses applied, host cell numbers, virus infection conditions, and promoters used. As a baculovirus system is a lytic system, engineered proteins often leak upon maturation of viral progenies, leading to loss of the proteins. Although the maturation times of the progeny viruses are similar, secondary infection complicates the peak time. This is especially evident when lower multiplicity of infection (MOI) is used. Accordingly, protein yield is not satisfactory. Second, conventional protein recovery methods also entail loss of engineered proteins. Numerous techniques have been developed to improve the yield of engineered protein (Kennedy, 1990; Garcia & Pires, 1993, and Terpe, 2003). Nonetheless, they are either expensive or labor consuming.
Thus, there is a need for a baculovirus expression system and method for efficient protein isolation.